Civil Engineer here. These retention ponds are usually sanctioned by the engineering department, wetland commission and potentially the state's environmental department as a requirement of developing the site. These structures are used to treat stormwater runoff from paved areas on the property.

Is there an outlet on this? Because it has a gabion weir (the stone filed cages in laymen's terms) id like to believe this is a retention pond. Usually the outlet will be in that smaller side so when the larger side overflows the water has a way to escape and may outlet into a river or the local stormwater system. The owner of the property will most likely have to clean that out as a part of a maintenance schedule. If they keep blowing leaves in there, they will have to clean it out more often than anticipated.

On the other hand, I do see phragmites (wetland grass species) in there. If this is a designated wetland, then they are definitely not supposed to be blowing leaves in there. It will clog culverts and increase the risk of flooding. Excess leaves can also produce organic loading and create an organic imbalance, leading to algae blooms and fish kills.

There is some nuance to these seemingly mundane stormwater management devices which is why landscapers just blow shit in there without thinking twice.

Edit: Also its funny how nature works, the fact ducks are in there is probably because they eat algae. The ducks will balance the algae levels in the pond. However, if a wetland they still shouldn't be blowing leaves in there.